Vinyl chloride based sols comprising a vinyl chloride based resin dispersed in a phthalic acid based plasticizer such as dioctyl phthalate (DOP) provide excellent workability and superior physical properties of the product film, and are consequently widely used in many industrial fields.
However, in recent years, with greater attention being paid to environmental issues, problems have arisen with vinyl chloride based sols due to toxic materials derived from vinyl chloride based resins, such as the generation of hydrogen chloride gas on incineration and the resulting damage to incinerators, acid rain, and the generation of dioxin during incineration.
Accordingly, plastisols using alternative resins to vinyl chloride based resins are being actively investigated.
Moreover, environmental issues have also been identified for many general purpose plasticizers such as the phthalate ester based plasticizers which are used in vinyl chloride based plastisols.
Based on this background, Japanese Unexamined Patent Application, First Publication No. Hei 7-53934 and Japanese Unexamined Patent Application, First Publication No. Hei 7-233299 propose acrylic plastisols using an acrylic based resin as an alternative to the vinyl chloride based resin. By using an acrylic based resin instead of a vinyl chloride based resin, these acrylic plastisols are novel proposals based on environmental concerns, and offer superior performance from an environmental viewpoint as they do not generate hydrogen chloride gas or dioxin even when incinerated.
However, these acrylic plastisols use a phthalate ester based plasticizer, and as such are unable to completely resolve all the environmental problems.
Japanese Unexamined Patent Application, First Publication No. Hei 10-231409 discloses an acrylic based plastisol which uses a benzoate ester based plasticizer as an example of an acrylic based plastisol which uses a plasticizer other than a phthalate ester based plasticizer. Furthermore, Japanese Unexamined Patent Application, First Publication No. Hei 8-100098 discloses an acrylic sol which uses a phosphate ester based plasticizer. In addition, Japanese Unexamined Patent Application, First Publication No. 2000-281857 discloses an acrylic based plastisol using a combination of an ether ester based plasticizer and a benzoate ester plasticizer. According to these proposals, because a phthalate ester based plasticizer is not used, environmental problems can be resolved.
However, the plasticizers disclosed in these patent applications display inadequate compatibility with the acrylic resin, and consequently, in gelled films formed with these types of acrylic based plastisols, the plasticizer exists in a free state within the gelled film. As a result, if the gelled film is used for a long period, or used under particular conditions such as high temperature conditions, the plasticizer travels to and then bleeds out from the surface of the gelled film. When the plasticizer bleeds out from the gelled film, the gelled film becomes brittle, and the mechanical characteristics such as the strength, the ductility, the flexibility, and the like tend to deteriorate. In addition, in cases in which ink or the like contacts the gelled film, the ink may transfer onto the gelled film.